Unregulated voltage converter with independent switching

ABSTRACT

An AC-DC voltage converter includes input terminals with a series circuit connected between the input terminals. The series circuit includes a switching element and a capacitor. The discharge of the capacitor supplies the output voltage of the converter. A control circuit controls the operation of the switching element so that the conducting state of the switching element is controlled exclusively as a function of the input voltage, while the nonconducting state of the switching element is controlled exclusively as a function of the output voltage. The converter has a good dynamic range and allows accurate measurement of current consumption at the output.

FIELD OF THE INVENTION

The invention relates to the field of electrical power converters, andmore specifically, to AC-DC conversion circuits using a principle ofintermittently charging a capacitor.

BACKGROUND OF THE INVENTION

Such converters are notably used directly for motorized products inbuildings, such as small screens for solar protection, venetian blinds,etc. They make it possible to convert the AC voltage from the powermains (“mains”) into a lower virtually DC voltage capable of being usedto supply an actuator with a low-power DC motor, for example of theCONCEPT-25 type product manufactured by the applicant. They may alsosupply only the control electronics of a more powerful AC motor, forexample, for roller shutters, or a single sensor combined with a radiofrequency receiver or transmitter.

These converters are termed “unregulated” because they operate withouttheir output voltage being tied to a fixed reference. This simplifiesthe structure of the converter and lowers the cost thereof At the input,these converters receive an AC current, which may or may not berectified; the half-wave or full-wave rectification of an AC current isconsidered in the present description as known in the art and is notdescribed. At the output, these converters provide a virtual DC voltagewith an amplitude less than the peak amplitude of the input voltage. Inthe remainder of the description, it is assumed that the input voltageis the mains voltage. This assumption is the most common forapplications in buildings. It is clear, however, that other applicationsare possible, and that the input AC current of the converter, whether ornot rectified, is not limited to the current supplied by the mains.These converters are called low-power converters, in that it is possibleto tolerate therein a lower conversion efficiency than in a high-powerplant, and therefore proportionally larger losses. The output power istypically less than 50 W.

In principle, as explained for example in FIG. 1 of U.S. Pat. No.4,641,233, the converters use the intermittent charging of ahigh-capacitance capacitor, hereinafter called C. In this context, theterm “high capacitance” refers to capacitances which are often greaterthan 100 μF. However, it will be understood that the capacitance of thecapacitor used is simply sufficient for maintaining enough outputvoltage between the periods of intermittently charging the capacitor. Asa result, the capacitance of the capacitor depends on the variation involtage accepted at the output of the voltage converter, on the outputcurrent needed, and on the charging frequency, which itself depends onthe input voltage frequency. For low output currents or for a highfrequency of the input voltage, a capacitor with a lower capacitance atthis threshold of 100 μF could be used. A switching element, hereinaftercalled Q, is placed between the half-wave or full-wave rectified mainsand this capacitor C, so as to charge the latter only during timeperiods when the mains voltage remains below a given threshold. For agiven load, it is thus possible to dimension C and to choose thethreshold voltage so as to comply with a given service voltage and agiven waveform at the output of the converter.

U.S. Pat. No. 4,001,668 (Lewis 1973) describes a device of this sort inFIG. 4. This patent emphasizes the very high tolerance to variations inthe mains voltage, allowing the use of such a circuit to supply a motorwith DC current whether power is provided by 110-120 V AC mains or from220-240 V AC mains.

The conducting and non-conducting states of the switching element Q (47)are completely determined by comparison of a voltage, which is an imageof the rectified voltage, with a threshold (50, 51, 45). It should benoted that the use of a current limiter formed by a resistor RP (48) andplaced upstream of the voltage measuring point makes it possible tobenefit from a cumulative effect favoring fast switching of Q from anoff state to a conducting state or vice-versa. In FIGS. 5 and 6, thispatent clearly indicates the pulsed shape of the line current (61, 65)and of the downstream voltage waveform at the terminals of the load(therefore at the terminals of C) (62, 66). Patents filed subsequentlyconstitute particular embodiments making it easier to control the switchQ, or improvements relating to the reduction of harmonics generated bycurrent spikes necessary for the periodic recharging of the capacitor.

GB-A-2 203 003 (Sanderson 1987) describes, in generic terms, a topologywhich is slightly different but based on the same principle. In FIG. 2,a current limiting device (11) is inserted between a switching elementformed by a field effect transistor and the capacitor (6), the voltagemeasurement for controlling the switching element being carried out on C(by means of the block referenced 10). This arrangement may remove thepossibility of a cumulative effect for the effective control of Q. Adevice (12) is intended to take the switching element out of servicewhen the voltage at its terminals exceeds a maximum threshold, however,this device is not described.

EP-A-0 763 878 (Helfrich 1995) describes, in FIG. 1, a convertertopology using a current limiting device RP (R1), a switching element Q(Q1) and a capacitor C (C2) with composite control of Q both by thevoltage upstream of RP (R6) and by the downstream voltage (R6). However,the voltage threshold is the same for the conducting and non-conductingstate of the switching element.

Other embodiments of converters using this intermittent charge principleare described in DE-A-44 44612, DE-A-31 44742, EP-A-0 399 598, DE-A-3245238, EP-A-0 249 259, FR-A-2 672 448, EP-A-0 500 113.

EP-A-0 622 889 (Wong 1994) describes a series topology (Q, C) without acurrent limiter. The input voltage V_(in)—the voltage of the rectifiedmains—is applied to the series circuit of the capacitor and of theswitching element. This circuit is intended to allow, as in the previouscases, double charging of C per half-cycle, and therefore to reduce thewaveform upstream of a regulator. The device analyzes both the voltageat the terminals of C (15) and the voltage at the terminals of Q (16). Qbecomes conducting if the voltage V_(cap) at the terminals of thecapacitor is less than a first given threshold. Q also becomesconducting if the voltage V_(ds) at the terminals of Q, which is thedifference between the rectified input voltage and the voltage at theterminals of the capacitor, becomes less than a second given threshold.In one half-cycle, this allows the capacitor to be charged when thevoltage increases from zero, then the capacitor to be charged when thevoltage decreases to zero.

U.S. Pat. No. 4,641,233 (Roy 1985) describes, with reference to FIG. 1,a similar topology. The switching device, a bipolar transistor, becomesconducting if the output voltage of the converter (downstream voltage)is less than the chosen reference voltage. However, the switching deviceonly becomes conducting if the voltage upstream of the switching elementis less than a voltage, which is about twenty volts for an outputvoltage of five volts. This is obtained using a second transistor, whichis switched on according to the input voltage, and which switches offthe first transistor when the input voltage is too high. According tothe patent, the objective of the second transistor is to preventdamaging the components as a result of switching at a high voltage.

A drawback of this device is that the threshold values for the inputvoltage and the output voltage are only approximately set. It is knownthat the conducting threshold voltage of a bipolar transistor or of asingle p-n junction are not accurately defined. The proposed solutioninvolves replacing the second transistor by a precisionreference-voltage source.

There is therefore a need for a converter, which makes it possible forthe switching element to be accurately controlled, allowing thecapacitor to be charged by the input voltage.

A second drawback of the circuit proposed by Roy is that it artificiallylimits the dynamic operating range at the output. This is because thiscircuit prevents the switching element from conducting as soon as theupstream voltage exceeds a fixed threshold, although it is quitepossible that when this threshold is reached, the capacitor C is not yetsufficiently recharged. This effect will occur on the rising edges ofthe rectified sinusoid. It is therefore beneficial in order to preventlimiting the dynamic operating range of the circuit to choose a highthreshold for the upstream voltage.

A third drawback of the circuit proposed by Roy appears on the fallingedges of the rectified sinusoid. This is because if the capacitor isdischarged, the switching element becomes conducting as soon as theupstream voltage goes below the fixed threshold. If this threshold forthe upstream voltage is high it becomes conducting at a higher voltagewhen going back below the threshold, this time during the falling edgeof the rectified sinusoid. This results in an operation which is moredamaging to the component, and therefore in overdimensioning thereof,and a risk of incompatibility with the electromagnetic compatibilitystandards. It is therefore beneficial to choose a low threshold for theupstream voltage.

The invention is based on the demonstration of these contradictoryrequirements in Roy's circuit and on the discovery of the correspondingproblem. There is therefore a need for a converter which does not limitthe dynamic operating range at the output, but which nevertheless allowsthe components to be protected, and which limits the risks ofelectromagnetic incompatibility. It would also be beneficial for theconverter to be able to measure the consumption of a device which itsupplies.

Moreover, it may be necessary to transmit a single signal over anelectrical line for supplying actuator(s) or sensor(s), which inparticular, may involve an alarm signal, a fault signal, or anacquisition signal in the actuator configuration phase, or a securitysignal for a sensor or the like. It is of course possible to use amedium other than the electrical supply line, for example radiotransmission, or a specific conductor for transmitting the signal.However, it is beneficial to use the electrical line, which avoidsproviding another medium. It has been proposed in U.S. Pat. No.3,852,740 (Haynes 1973), U.S. Pat. No. 4,121,201 (Weathers 1974) or elsein U.S. Pat. No. 4,755,792 (Pezzolo 1987) to use carrier currenttechnologies to transmit a signal over a supply line. These technologiesare complex and their reliability is not guaranteed if carried out atlow cost. They are not suitable for very limited data transmission.There is therefore a need for simple and reliable transmission of asignal, over the supply line of an actuator or a sensor.

FR-A-2 785 735 discloses a voltage converter. The converter has acapacitor, which is charged at most once per half-wave of the rectifiedinput AC voltage, close to the beginning of the half-wave. Specifically,the rectified input AC voltage is applied to the capacitor through aswitch. The switch is controlled to be opened whenever the outputvoltage across the capacitor is higher than a first threshold. Theswitch is controlled to be closed whenever the difference between theinput voltage and the output voltage is higher than a second threshold,which may be zero. Thus, the switch is closed not exclusively based onthe input voltage, but rather according to the difference between theinput voltage and the output voltage. This may cause damage to thecomponents of the converter if the switch is closed while the inputvoltage is high.

U.S. Pat. No. 5,818,708 discloses a voltage converter. Rectified inputAC voltage is applied to a load capacitor through a switch. The switchis controlled by a latch circuit. The switch is turned on upon receivinga set input, and is turned off upon receiving a reset input. The setinput of the latch is connected to a first voltage sensor, which sensesthe voltage provided by the rectifier. The reset input of the latch isconnected to a second voltage sensor, which senses the voltage acrossthe load capacitor. The first voltage sensor enables the set input ofthe latch when the voltage provided by the rectifier is higher than alow (typically zero) voltage. This turns the switch on. The secondvoltage sensor enables the reset input of the latch when the voltageprovided by the rectifier is higher than the desired output voltage,which turns the switch off. In this converter, the capacitor isexclusively charged on the rising edge of the input voltage.

SUMMARY OF THE INVENTION

In one embodiment, the invention therefore provides a voltage converterwith input terminals, a series circuit between the input terminals, theseries circuit comprising a switching element and a capacitor. Thedischarge of the capacitor supplies the output voltage of the converter.The circuit also comprises a control circuit of the switching element,which controls the conducting state of the switching element exclusivelyas a function of the input voltage and controls the non-conducting stateof the switching element exclusively as a function of the outputvoltage.

Advantageously, the control circuit controls the conducting state of theswitching element when the input voltage is less than a first threshold,and controls the non-conducting state of the switching element when theoutput voltage is greater than a second threshold. In this case, thefirst threshold may be higher than the second threshold so that thecapacitor is charged on both rising and falling edges of the inputvoltage.

In another embodiment, the invention therefore provides a voltageconverter with input terminals, a series circuit between the inputterminals, the series circuit comprising a switching element and acapacitor. The discharge of the capacitor supplies the output voltage ofthe converter. The circuit also comprises a control circuit of theswitching element. This circuit sets the switching element to theconducting state when the input voltage is less than a first threshold.It also sets the switching element to the non-conducting state when theoutput voltage is greater than a second threshold, which is lower thanfirst threshold

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will becomeapparent on reading the following description, given by way of exampleand with reference to the drawings which show

FIG. 1, a schematic view of a specific embodiment of a converteraccording to the principle of the invention;

FIG. 2, a graph of the input voltage, of the control voltage and of theinput current in the converter of FIG. 1, as a function of time;

FIG. 3, a schematic view of a specific embodiment of a converteraccording to a preferred embodiment of the invention;

FIG. 4, a more detailed view of a converter of the type in FIG. 2;

FIG. 5, a representation of a conventional rectifying circuit supplyingpower to a load RU, with filtering by a capacitor;

FIG. 6, a graph of the output voltage of the circuit of FIG. 4;

FIGS. 7 and 8, schematic views of specific embodiments ofmicrocontrollers capable of being used according to the invention in itsapplication to measuring the current output in the downstream direction(or output current);

FIG. 9, a graph of the input current to a converter, in a firstoperating state of a device connected to the converter;

FIG. 10, a graph of the line current supplied to three converters, whenthe devices connected at the output of these converters are all in afirst operating state;

FIG. 11, a graph of the line current supplied to three converters, whentwo of the devices connected at the output of these converters in afirst operating state while the third device is in a second operatingstate; and

FIG. 12, a schematic representation of a detector for detecting a changeof operating state of a device connected to an output of this converter.

DESCRIPTION OF THE INVENTION

The invention provides an AC-DC voltage converter with input terminals,a series circuit between the input terminals, where the series circuitcomprises a switching element and a capacitor delivering the outputvoltage. The converter further comprises a circuit for controlling theswitching element. The control circuit controls the conducting state ofthe switching element exclusively as a function of the input voltage andcontrols the non-conducting state of the switching element exclusivelyas a function of the output voltage.

As the non-conducting state of the switching element is exclusively afunction of the output voltage, the switching element remains conductingwhen the output voltage is too low, independent of the value of theinput voltage applied to the terminals of the series circuit. Thecapacitor continues to be charged as needed, even if the input voltageexceeds a threshold value. The converter provided therefore has a largerdynamic range than in the solution disclosed in U.S. Pat. No. 4,641,233or GB-A-2 203 003. This is because the dynamic range of the outputvoltage of the converter is not limited by a threshold value of theinput voltage.

As the conducting state of the switching element is exclusively afunction of the input voltage, it is possible to protect the componentsof the circuit against any damage resulting from a conducting stateunder a high input voltage. It is therefore not necessary to“overdimension” or “over-design” the components of the converter, and itis possible to limit the risk of electromagnetic incompatibility. Use ofoverdimensioned components, or in other words, components having higherratings than needed, may be uneconomical

The control circuit may control the conducting state of the switchingelement when the input voltage is less than a first threshold V1. Thismakes it possible to use simple elements for making the control circuit.This is also the a simple embodiment where the control circuit passesthe switching element to the conducting state exclusively as a functionof the input voltage.

Similarly, the control circuit may control the non-conducting state ofthe switching element when the output voltage is greater than a secondthreshold V2. This is also a simple embodiment where the control circuitpasses the switching element to the non-conducting state exclusively asa function of the output voltage.

Selecting a first threshold value higher than the second threshold valuemakes it possible to charge the capacitor not only on the rising edge ofthe input voltage, but also on the falling edge of the input voltage.This increases again the dynamics of the converter and the ability ofthe converter to provide the output current. As discussed below, thiscondition, however, is not necessary, e.g., for measuring the powerdelivered by the converter as discussed in reference to FIG. 5 andfollowing.

FIG. 1 shows a schematic view of a converter according to one embodimentof the invention. At the input (or upstream), the converter receives anAC voltage rectified by any suitable means, as shown diagrammatically inthe figure in the case of full-wave rectification. This voltage isapplied to a resistive or inductive current limiting element 2, thefunction of which is to limit the current flowing through the switchingelement and the capacitor when the switching element is conducting.Moreover, the current limiting element is connected to the seriescircuit of the switching element 4—an MOS transistor in the example—andof the capacitor 6. The terminals of the capacitor form the outputterminals of the converter. In the figure, the voltage at the terminalsof the series circuit of the switching element and of the capacitor isreferenced U_(e), which subsequently will be termed the upstreamvoltage, or input voltage. In the figure, the voltage at the terminalsof the capacitor is referred to as U_(s), which subsequently will alsobe termed the downstream voltage or output voltage. The converter alsocomprises a control circuit 8. The control circuit is connected to thecontrol input of the switching element. Moreover, it receives thevoltage U_(e) and the voltage U_(s). For this purpose, in the schematiccircuit of FIG. 1, the control circuit has first and second inputterminals respectively connected between the current limiting element 2and the switching element 4, and between the switching element 4 and thecapacitor 6 on the other hand.

The control circuit comprises a first comparator 10, the inverting inputof which is connected to the first input terminal, and to thenon-inverting input of which a first reference voltage V1 is applied.The output of the first comparator is applied to the set input S of alatch 14. The control circuit comprises a second comparator 12, thenon-inverting input of which is connected to the second input terminal,and to the inverting input of which a second reference voltage V2 isapplied. The output from the second comparator is applied to the resetinput R of the latch 14. The output from the latch provides the controlsignal delivered by the control circuit, and is therefore connected tothe control input of the switching element 4.

The converter of FIG. 1 operates as follows. It is assumed that theswitching element is conducting. The capacitor 6 is charged by thecurrent passing through the limiting element, the switching element, andthe capacitor. When the voltage U_(s) at the terminals of the capacitorexceeds the second reference voltage V2, the latch 14 changes state, andthe switching element 4 becomes non-conducting. The charging of thecapacitor ceases. Thus, the capacitor by the input voltage ceasescharging as soon as the voltage at the terminals of the capacitorexceeds a limiting value dictated by the second reference voltage V2.Further, the non-conducting state of the switching element dependsexclusively on the voltage U_(s), but does not depend on the voltageU_(e). This is not a problem. In fact, when the switching element isconducting, the voltage at its terminals is obviously zero (or verylow), and making it non-conducting does not subject it to any particularstress, and does not cause problems from the EMC point of view. Ofcourse, the switching element Q should preferably be able to withstand avoltage equal to the amplitude of the mains voltage. Here it isunderstood that the current limiting element could be omitted from thecircuit of FIG. 1. Moreover, in the presence of this current limitingelement, the value of the current flowing in the switching element islimited by the element 2. This may make it easier to dimension theswitching element so that it withstands passage of the capacitorcharging current.

Starting from this state, when the upstream voltage U_(e) goes below thefirst reference voltage V1, the first comparator applies a signal to theset input of the latch, and the latch changes to a new state. Theswitching element is then turned on. As the conducting state does notdepend on the downstream voltage, but only on the upstream voltage, itis possible to select the time at which it is made conducting, such thatthe voltage at the terminals of the switching element is as small asdesired.

The circuit of FIG. 1 therefore makes it possible to preserve thedynamic range of the converter, and to protect the components. Ittherefore mitigates the second and third drawbacks of the Roy circuit,as explained above.

In the example of FIG. 1, the output voltage is measured at theterminals of the capacitor 6, and the input voltage is measured at theterminals of the series circuit of the switching element and of thecapacitor. It will be noted that when the switching element is notconducting, the voltage at the terminals of the current limiting elementis zero. As such, the input voltage may be measured equally at theterminals of the series circuit of the switching element and of thecapacitor, or at the terminals of the circuit having the currentlimiting element, the switching element, and the capacitor in series.Similarly, when the switching element is conducting, the voltage at theterminals of the series circuit of the switching element and of thecapacitor is equal to the voltage at the terminals of the capacitor 6,ignoring the voltage drop at the terminals of the switching element 4.Thus, if it is known when the switching element is conducting, it ispossible to use the voltage at the terminals of the series circuit ofthe switching element and of the transistor to control thenon-conducting state. More generally, the point of measuring the inputvoltage and the output voltage may vary depending on the solutions givenin the examples of the figures.

In this embodiment, the converter also mitigates the first drawbackbecause the switching times do not depend on the properties of theswitching element. It would also be possible to use a converter of thetype of FIG. 1 with a switching element of another type.

FIG. 2 is a graph of the upstream voltage U_(e) and of the controlvoltage U_(c) in the converter of FIG. 1, as a function of time. In theexample of this figure, the first reference voltage V1 is higher thanthe second reference voltage V2. This ensures that the capacitor isloaded not only on the rising edge of the rectifier input voltage, butalso on the falling edge of the rectified input voltage.

The control voltage U_(c) is the output voltage of the control circuit,applied to the control input of the switching element. The graphcorresponds to the example of full-wave rectification, and shows severalhalf-cycles. The upstream voltage or input voltage U_(e) has beenplotted in dotted lines on the figure; at time t=0, the input voltage isa maximum, and it is assumed that the switching element is notconducting. On the falling edge of the first half-cycle, the switchingelement becomes conducting at time t₁ when the upstream voltage U_(e)goes below the first reference voltage V1. The capacitor is charged onthe falling edge of the first half-cycle until the upstream voltageU_(e) becomes less than U_(s), and on the rising edge of the secondhalf-cycle, as soon as the upstream voltage U_(e) exceeds U_(s) anduntil the downstream voltage reaches the threshold value V2, at time t₂.This time depends on the rate of charging of the capacitor, andtherefore on the downstream consumption of the converter. The operationis similar on the falling edge of the second half-cycle, and on therising edge of the third half-cycle, becoming conducting at time t₃ andnon-conducting at time t₄.

It is assumed that the consumption of the device placed downstream ofthe converter then increases. On the falling edge of the thirdhalf-cycle, the switching element is switched on at time t₅, independentof the consumption. On the rising edge of the fourth half-cycle, thecapacitor is charged more slowly because of the consumption of thedevice placed downstream of the converter. The threshold voltage V2 isonly reached at a time t₆, with a charging duration t₆-t₅, which isgreater than the charging duration t₄-t₃ during the previouscancellation of the voltage. The same phenomenon is found on the risingedge of the following half-cycle, at time t₈.

The graph also shows the control voltage U_(c). It is found that thiscontrol voltage U_(c) has marked rising and falling edges, which arerepresentative of the times at which the switching element becomesconducting and non-conducting. The circuit therefore provides avoltage-calibrated signal (0±V), which exactly indicates the start andfinish times at which the switching element becomes and ceases to beconducting. The duration for which this signal remains at the high levelis representative of the downstream consumption of the converter.

It is also found that the times t₁, t₃, t₅ and t₇ of becoming conductinghave a temporal position which is fixed with respect to the voltagehalf-cycles applied to the converter. This is explained by the fact thatbecoming conducting depends only on the voltage applied to the input ofthe converter, and does not depend on the output voltage. However, thetimes t₂, t₄, t₆ and t₈ at which the switching element becomesnon-conducting are a function of the downstream voltage and of theoutput consumption of the converter. The circuit of FIG. 1 makes itpossible, by analyzing the temporal position of these times t₂, t₄, t₆or t₈, to measure the output consumption of the converter. This isexplained in more detail below with reference to FIG. 5. This analysismay be carried out by measuring the time between the rising and fallingedges of the control voltage.

Finally, the graph shows the shape of the line current, i, supplying theconverter. In the vicinity of the zero voltage points, the graph isapproximated. Depending on the consumption, the current has a waveformiL₁ or iL₂.

FIG. 3 is a schematic view of a converter according to a preferredembodiment of the invention. The example of FIG. 3 makes it possible touse a control circuit having a single input, while ensuring that thecontrol circuit controls the conducting state (and the nonconductingstate, respectively) from just one of the upstream and downstreamvoltages. This has the advantage of simplifying the converter structure.Furthermore, the circuit of FIG. 3 makes it possible to use a singlevoltage reference instead of the two voltage references shown in FIG. 1.The circuit of FIG. 3, like that of FIG. 4, uses an MOS transistor as aswitching element. This MOS transistor is an example of a switchingdevice which has a substantially constant conducting threshold betweenits control and output terminals, and only becomes conducting betweenits input terminal and its output terminal when this threshold isreached. As this threshold is constant when the transistor isconducting, the voltage U_(gm) between the transistor gate and earth isequal to the sum of the output voltage U_(s) and the conductingthreshold VT of the transistor. The output voltage may therefore bemeasured, implicitly, from the output voltage of the control circuit,applied to the gate of the transistor.

In FIG. 3, the elements already described with reference to FIG. 1 canbe recognized, which elements bear the same reference numbers and willnot be described again. The switching element comprises an inputterminal D, an output terminal S, and a control terminal G, the controlvoltage being applied between G and S, with the property of having asubstantially constant conducting threshold VT between control G andoutput S terminals so that it becomes conducting between D and S whenthis threshold VT is reached.

The control circuit 20 has a single input connected between the currentlimiting element 2 and the switching element 4. Furthermore, it isconnected to earth (also referred to as ground). The control circuitcomprises a voltage source 22, which may be driven by the control input.The voltage provided by the source remains virtually constant while theinput voltage of the control circuit, which is also the input voltageapplied to the device, is greater than a first threshold, and otherwisedecreases. FIG. 4 shows a practical implementation of such a voltagesource. The control circuit further comprises a second capacitor 24 anda controlled inverter 26. The second capacitor has a memory function andhas a terminal connected to the earth of the control circuit. The otherterminal of the capacitor 24 is connected to the input terminal of thecontrolled inverter 26.

In its schematic representation, the controlled inverter is similar to asingle-pole double-throw switch. The controlled inverter includes aninput terminal, which is connected to the capacitor 24. Toggling or“moving” between the first and second position of the controlledinverter 26 essentially reciprocally couples the input terminal of thecontrolled inverter to either the control G of the switching element 4,or to the terminal of the voltage source, as shown in FIG. 3.

In one specific embodment, a mechanical device having a wiper orcomponent that physically moves or toggles may be used. Such a devicemay be a mechanical switch, a digitally controlled analog switch orequivalent device, as is known in the art. Preferably, such a mechanicaldevice may be used only if the switching frequency of the controlledinverter was sufficiently low.

Alternatively, according to another specific embodiment, the controlledinverter may be a solid state device, such as a solid state switch. Thismay be a digitally controlled operational amplifier arranged to have aunity gain. Thus, such amplifiers act as an analog transmission gate.Moreover, digitally or analog controlled analog transmission gates mayalso be used, as is known in the art. Note, that the control input tothe switching device, whether such control input or signal is analog ordigital, is not specifically shown in FIG. 3, as operation of such acontrolled inverter is known in the art.

The controlled inverter 26 alternates between the first and the secondposition. In the first position, the controlled inverter connects thesecond memory capacitor 24 to the voltage source 22. In the secondposition, the controlled inverter connects the second capacitor 24 tothe output of the control circuit. Toggling or switching from the firstto the second position takes place when the voltage from the voltagesource 22 decreases. Toggling from the second to the first positiontakes place when the difference between the output voltage of thecontrol circuit and the output voltage of the converter becomes lessthan the conducting threshold of the switching element.

The operation of the circuit of FIG. 3 is as follows. It is assumed atthe start that the input voltage of the control circuit is greater thanthe first threshold V1, the switching element being assumed to benon-conducting. Since the input voltage of the control circuit isgreater than the first threshold, the controlled inverter 26 is in thefirst position, and the second capacitor 24 is charged by the voltagefrom the source 22. There is no signal applied at the output of thecontrol circuit to the control input of the switching element 4, whichtherefore remains nonconducting. When the input voltage decreases andgoes below the first threshold, the voltage from the source 22decreases, and the controlled inverter 26 goes into the second position.At this point, the memory capacitor 24 is connected to the output of thecontrol circuit, and therefore applies a voltage to the control terminalG of the switching element. The switching element therefore becomesconducting; it is understood here that the memory capacitor is chosen soas to provide a voltage greater than the conducting threshold of theswitching element, and this as soon as it is charged, even for a briefduration, by the source 22. It is also understood that the conductingstate of the switching element depends only on the upstream voltageapplied at the input of the control circuit when the switching elementis not conducting.

Once the switching element becomes conducting, it remains conductingunder the action of the memory capacitor 24 while the controlledinverter is in the second position. When the difference between theoutput voltage of the control circuit and the output voltage of theconverter becomes less than the conducting threshold of the switchingelement, the inverter 26 goes from the second position to the firstposition. The switching element is then isolated. It is understood thatthe non-conducting state of the switching element depends only on theoutput voltage at the terminals of the capacitor, as measured across theoutput of the control circuit given the conducting threshold of thetransistor, but does not depend on the input voltage applied to theconverter.

Thus, as in the circuit of FIG. 1, the switching element becomesconducting as a function of the input voltage, but not as a function ofthe output voltage. The switching element becomes non-conducting as afunction of the output voltage, but not as a function of the inputvoltage.

FIG. 3 complies well with the principle of FIG. 1, with a first implicitcomparator monitoring the upstream voltage, via the driven voltagesource and a second implicit comparator monitoring the downstreamvoltage via the voltage between G and S of the switching element.

In this specific embodiment, the first reference voltage, under whichthe switching element is conducting, may also be higher than the secondreference voltage. This again makes it possible to load the capacitor inboth the falling edge and the rising edge of the rectified inputvoltage.

FIG. 4 shows a more detailed view of a converter of the type of FIG. 2.The current limiting element, the switching element, the capacitor 6,the control circuit 20 and its second capacitor 24 will be recognized.The input of the control circuit (called A in the figure) is connectedto earth through the series circuit of resistors R2 and R4 referenced 28and 30. A Zener diode 32 connects the common terminal of the resistors28 and 30, called B in the figure, to earth. This point B is alsoconnected to one terminal of the second capacitor via a diode which isforward biased from B towards the second capacitor. The transmitter of atransistor 36 is connected to the second capacitor 24; the base of thistransistor is connected to the point B through a resistor R5 referenced38. The collector of the transistor is connected to the control input Gof the switching element 4 and to earth through a resistor R3 referenced40.

The voltage U1 is provided by the voltage source to the point B. Whenthe voltage U1 is applied between the control input G of the switchingelement and earth, the switching element Q conducts if the voltage UGSis greater than or equal to the conducting threshold, therefore whilethe output voltage US is less than U1−VT. The downstream threshold V2 isin this case therefore equal to U1−VT. The value U1 is determined for agiven threshold, and for a given MOS.

In the circuit of FIG. 4, the inverting contact K is in fact produced bycombining the diode 34, the transistor 36 and the resistor R5 38. Thesecond capacitor 24 is charged by placing the latter in parallel withthe Zener diode 32, through the diode 34.

It will be assumed for the sake of clarity that the voltage at theterminals of the diode 34 when it is conducting is very small comparedto the Zener voltage VZ of the Zener diode 34. Therefore, we simply haveU1=VZ=V2+VT. The value of the Zener voltage is therefore chosen as afunction of the conducting threshold of the switching element 6, and ofthe second reference threshold V2 (or downstream threshold), above whichthe switching element becomes non-conducting.

The second transistor 36 is always off, unless the potential at Bbecomes less than that at E. The latter situation is encountered whenthe Thevenin generator equivalent of the assembly (UA, R2, R4) has avoltage less than VZ.

If, following the decrease of UA on a falling edge of the rectifiedhalf-sinusoid, the voltage U1 becomes less than the Zener voltage VZ,then the second transistor starts to conduct, leading to the switchingelement starting to conduct. If the switching element starts to conduct,the potential of A decreases, and therefore that of B also decreases,which further reinforces the conduction of the second transistor, etc.There is therefore a cumulative effect.

At the virtual instantaneous moment when the second transistor and theswitching element become conducting, the potential of A goes from thethreshold value V1 to the value U_(s) (voltage at the terminals of C),thus confirming the conduction of the second transistor and switchingoff of the diode 34.

For a given Zener voltage VZ, and for a chosen threshold V1, the valuesof resistors R2, R4 to be used are calculated from the equation:${V1} = {{\frac{{R2} + {R4}}{R4}\quad {VZ}} = {\frac{{R2} + {R4}}{R4}\left( {{V2} + {VT}} \right)}}$

By choosing suitable resistors R2 and R4, the circuit makes it possiblefor the upstream and downstream thresholds V1 and V2 to be chosen freelyAgain, one may select V1 higher than V2 for ensuring that the capacitoris loaded on both the falling and rising edges of the input voltage.

The voltage UGM at the terminals of the resistor R3 40 remains equal toVZ during the conduction duration, if the time constant R3*C2 is highcompared to the period, where C2 is the capacitance of the secondcapacitor.

When the voltage at the terminals of the capacitor 6 increases enough toreach VZ−VT, then the conduction of the switching element tends todecrease, and UA increases. The second transistor tends to conduct less,etc. There is a cumulative effect in the other direction: the switchingelement and the second transistor switch off. The voltage UGM istherefore switched off. There is therefore, if necessary, avoltage-calibrated signal, UGM, representative of the conductionduration, as explained with reference to FIG. 2.

The circuit of FIG. 4 provides a simple solution for implementing thediagram of FIG. 3. Of course, other solutions are possible withoutdeparting from the scope of this invention.

Applications of the circuit of FIGS. 1 to 4 to measuring the downstreamconsumption of the converter—FIGS. 7 and 8—or to transmitting data alonga supply line—FIG. 9 onwards, will now be described with reference toFIG. 5.

FIG. 5 shows a representation of a conventional rectifying circuit,which supplies power to a load RU, with filtering by a capacitor. Thecircuit comprises a diode 42 providing half-wave rectification, acurrent limiter formed by a resistor 44, and a parallel circuit of acapacitor 46 and of an output load RU referenced 48. The output voltageU_(s) is the voltage at the terminals of the capacitor. FIG. 6 is agraph of the output voltage of the circuit of FIG. 5. A half-cycle ofthe voltage applied at the input to the circuit is shown in solid line,and the theoretical maximum amplitude at the terminals of the load,which is calculated from the previous curve by reducing the ratioRU/(RP+RU), is shown in dotted line, while the output voltage is shownin bold line. In such a circuit, it is known that the waveform of theoutput voltage U_(s) is directly related to the current absorbed by theload arranged in parallel on the capacitor. The exact measurement ofsuch a waveform is enough to determine this current, either bycalculation, or from a calibration curve. However, this measurementrequires knowing both the minimum and maximum of the voltage graphU_(s), identified by their horizontal tangents in FIG. 6. This involvescontinuous sampling of the output voltage so as to determine the minimumand maximum of the output voltage.

Conversely, as explained with reference to FIG. 2, the control voltageof the switching element in the circuit of FIG. 1, 3 or 4 has risingedges in a temporal position which is fixed with respect to the timewhere the voltage is zero, and falling edges whose position isrepresentative of the consumption downstream of the converter. It istherefore possible, by measuring the switching times of the switchingelement, to determine the consumption downstream of the converter. Thisonly depends on the second reference voltage to which the output voltageis compared for opening the switching element. Therefore, such powerconsumption measurement is possible even where the first referencevoltage to which the input voltage is compared for closing the switchingelement, is lower than the second reference voltage.

FIGS. 7 and 8 show schematic views of microcontrollers adapted to beused according to the invention in its application to measuring thecurrent output downstream of the converter. FIG. 7 shows amicrocontroller which receives as an input the control voltage U_(c)shown in FIG. 2. The microcontroller is adapted to measure the durationfor which this control voltage remains at a high level. What is requiredis for this is to count the pulses of an internal clock, the counterbeing activated during the high state of the control voltage. Asindicated with reference to FIG. 2, this duration is representative ofpower consumption downstream of the converter. The circuit of FIG. 7allows a simple measurement of the consumption, without it beingnecessary to sample the signal in order to determine its minima and itsmaxima.

FIG. 8 shows another circuit based on the observation that in theconverter of FIG. 1, 3 or 4, the extrema of the output voltage arereached at the times of switching the switching element, and that theseswitching times are accurately provided by the rising and falling edgesof the control voltage of the switching element. The microcontroller ofFIG. 8 therefore receives as inputs the control voltage and the outputvoltage of the converter. The output voltage is applied to an analoginput. In a first example, the control voltage U_(c) activates aninterrupt of the microcontroller. The latter then measures the outputvoltage only on the rising and falling edges of the control voltage. Ina second example, the control voltage U_(c) directly activates thesampling control on its rising and falling edges. In one case as in theother, the output voltage does not have to be continuously sampled fordetermining its extrema, and it is possible to easily determine powerconsumption downstream of the converter. The converter proposed abovetherefore makes it possible to measure the consumption more simply,without requiring complete sampling of any signal

FIGS. 9 and following describe downstream operating methods applicableto devices such as actuators, to which power is supplied by converterssuch as described in reference to FIGS. 1, 3 and 4. These methods enabledata to be transmitted from the devices. One or more converters of thetype described above is or are assumed to be connected to the same powersupply line on the AC mains. The problem, as stated above, is totransmit a signal upstream from one of the converters, for example, tothe electrical switchboard of the supply line. The actuators using aconverter according to the invention are, for example, motors comprisingcontrol electronics, to which power is supplied by the converters. Theterms “load” or “actuator” are also used herein to designate devicesconnected at the output of the converters, and to which power issupplied by the converters.

The solution proposed here is based on the observation that the currenti_(e) input to the converter, shown in FIG. 2, has rising and fallingedges coinciding with the rising and falling edges of the controlsignal. The timing of these current edges is therefore alsorepresentative of the consumption of a device connected to theconverter. A variation in consumption may be detected upstream by asimple measurement of the current supplied to the converter.

At rest, each device receives a current and therefore causes upstream ofthe converter a line current or input current i_(e) whose shape is shownin FIG. 5 of Lewis, or in FIG. 2 of EP-A-0 763 878 (Helfrich 1995). Thiscurrent is in the form of a series of pulses, 2 or 4 pulses over oneperiod of the mains, as a function of half- or full-wave rectification.As explained above, for the dual-threshold converters of the typedescribed in FIGS. 1, 3 and 4, the duration of the pulse (or of the dualpulse) is the same as that of the control voltage. This duration isdirectly related to the consumption of the converter and of itsassociated load.

In the case of full-wave rectified devices, a first waveform iL₁ of theline current i_(e) will be attained for the rest state, and a secondform iL₂ of this current will be attained in the active state, as shownin FIG. 2. The over-consumption may be due, for example, to the factthat the device in the active state supplies a relay coil enabling themotor of the actuator. It is possible for the consumption to bedetermined remotely from the pulse shape. It is possible to measure theduration of each pulse. It is also possible, since each pulse starts ata particular temporal position, to measure the time difference betweenconsecutive pulses. Thus, the difference between the falling edge of onepulse and the rising edge of the following pulse is measured. In theexample of FIG. 2, a duration T₁=t₃−t₂ is obtained for a firstconsumption, and a duration T₂=t₇−t₈ is obtained for a secondconsumption. It should be noted that if the supply device controls amotor, the total line current i_(e) then corresponds to thesuperposition of the current iL₂ and of the current iM absorbed by themotor, this latter current being sinusoidal.

It is therefore clearly possible, by measuring the current supplied to aconverter to determine the consumption of a device connected to theoutput of this converter. This enables data to be transmitted, by actingon the consumption of the device in order to vary the current suppliedto the converter. It is therefore possible to transmit data from adevice connected a the output of a converter to any point of the linesupplying the converter with AC current.

By way of example, it is possible to detect an alarm or a fault in thedevice to which power is supplied by the converter. All that is requiredfor this is that the consumption of the device varies in the case of analarm or fault. For example, provision may be made for the device to beprogrammed to supply power to a passive element in the case of an alarmor fault, or more generally, of data to be transmitted. Thecorresponding variation in duration between pulses of the input to theconverter enables the alarm or the fault to be remotely detected. Inthis case, an over-consumption, i.e. an increase in the pulse durationor a reduction in the duration separating the pulses, is detected. Itcould also be decided to decrease the consumption, either deliberatelyor simply by taking the device out of the circuit, which would have theeffect of decreasing the pulse duration, or of increasing the durationbetween two successive pulses.

The method also functions in the presence of a plurality of convertersand of associated devices, connected in parallel on the same powersupplying line. The converters and the devices may be identical, or atthe very least, may have identical pulse durations. It is assumed thatthe devices are at rest, i.e. in the state where the duration betweenpulses is T₁. As explained above, it would also be possible to considerthe pulse duration. The duration between pulses is considered by way ofexample herein. The superposition of the rest currents of all thedevices causes a resulting pulsed current of higher amplitude, theamplitude being given by the sum of the amplitudes of the variousindividual currents, but still characterized by the duration T₁.

FIG. 9 shows a partial graph of the input current to a converter, in afirst operating state, characterized by a duration T₁ between twopulses. In the figure, only the end of one pulse and the start of thefollowing pulse are shown. FIG. 10 shows a graph of the current input tothree identical converters, all in the same first operating state. Asindicated above, the duration between two pulses is still T₁—but theamplitude of the current is higher.

Now it is assumed that an alarm, a fault or a motor start-up, isdetected by one of the devices. The latter is, for example, programmedto supply power to a passive element upon a fault, which causes anover-consumption characterized by a duration T₃ between two pulses,where T₃<T₁, according to the measurement convention adopted. A currenthaving the shape shown in FIG. 11 is then measured on the supply line.The time between successive pulses is now T₃, at least when the currentis nearly zero.

It is possible to take a duration T₃ equal to the duration T₂corresponding to another operating mode. Similarly, two different valuesmay be preferred. If a duration T₃=T₂ is taken, the difference betweenstarting up a device, which leads to an over-consumption and a reductionin the duration at T₂—and an alarm, which has the same effect, cannot bedistinguished. If the two durations are different, it is possible todifferentiate between start-up of a device and an alarm generated bythis device. It is understood that it is generally possible to detect avariation in consumption, and that this variation may take differentvalues depending on requirements. It could be possible, for example, togenerate various over-consumptions using various passive elements, byconnecting one or more of these elements to the output of the converter.This is only one example of a code allowing transmission of data from adevice supplied in power by the converter through the supply line of theconverter. It is possible to choose various over-consumptions for thedevices supplied by the various converters. This would make it possibleto identify, in the case of data transmission by a device, which of thedevices has transmitted the data, by a single measurement of theduration separating the pulses. It would also be possible to detect asimultaneous alarm on various converters, if required, by analyzing thepulse shape.

Upstream, a pulse-width detector or a detector of the time separatingthe pulses may be used for detection. Such a detector is placed upstreamon the common input line. This detector may be designed to be activatedas soon as the current exceeds a given threshold, less than theamplitude of the pulses produced by just one of the devices at rest. Thetime measurement may be carried out by a microcontroller. If necessary,synchronization on the mains removes any ambiguity, this synchronizationbeing even simpler because the timing of the rising edge of a currentpulse relative to the sinusoidal input voltage is known.

Producing the detector calls on known techniques. FIG. 12 shows anexample of a detector. The latter comprises an optical coupler 50, withenough gain to work in saturation when just one of the devices issupplied, with its rest consumption. Diodes 52, 54, 56 placed inparallel on the LED of the optical coupler make it possible to divertthe current when it exceeds the level which the LED can withstand. Thevoltage measured at the terminals of the optical coupler provides asignal representative of the current.

The current sensor may also be a pulse transformer, or any devicecapable of eliminating the 50 (60) Hz or 100 (120) Hz components,highlighting the sharp edges at the start and end of the pulses. It thenbecomes possible to detect data, even superimposed on the supply current

In this case, this situation is all the more advantageous since theprinciple of power supply ensures that the current spikes are located attimes close to the time when the main voltage goes to zero; this isfavorable to the measurement.

The alarm or fault detection electronics compares the duration Tmeasured to a fixed threshold TA between the values T₁ and T₃. Theduration T₁ may be acquired by learning. The discrimination threshold ofan alarm, TA, is deduced therefrom by a given offset.

In a product configuration phase, the state feedback may also be encodedby a series of different states T₁, T₃. From this point of view, it isclear that the second embodiment, with temporal detection, hasadvantages. Furthermore, it should be noted that this form makes itpossible to discriminate clearly between a consumption state leading toa duration T₃ (alarm) which is different from T₁ (rest) and T₂ (motoractuation). Under these conditions, the fault detection can becontinuously active, without it being necessary to validate it by analarm or detection mode under overall control. Finally, the secondembodiment lends itself more easily to encoding the transmission of aseries of binary data, as described in Pezzolo.

Of course, the invention is not limited to the embodiments given above.Thus, the load capacitor may be produced in different ways, and mayinclude, for example, several discrete components. Functionally, it is acapacitor, and it is therefore denoted as such. Similarly, the currentlimiting element may also comprise one or more coils with one or moreiron cores. In the examples, the terminals of the capacitor constitutethe output terminals of the converter; there is nothing to prevent otherelements being provided in parallel or in series with the capacitor,since the output voltage arises from discharging the capacitor.

It is indicated above that the conducting state of the switching elementdepends “exclusively” on the upstream voltage, or input voltage, orrectified input voltage. It is also indicated that the non-conductingstate depends “exclusively” on the downstream voltage, or outputvoltage, or voltage at the terminals of the capacitor. In either case,this may not be exactly precise because both the conducting state andthe non-conducting state may depend on other factors, for example,reference voltages V1 and V2 in the circuit of FIG. 1, the values of theresistors forming the voltage divider, or other factors. It is thereforenecessary to understand the term “exclusively,” as used herein, meansthat the conducting state depends on the upstream voltage, without beinga function of the downstream voltage, and that the non-conducting statedepends on the downstream voltage, without being a function of theupstream voltage.

In the circuit of FIGS. 1, 3 and 4, the current limiter is locatedupstream of the series circuit of the switching element and of thecapacitor, and upstream of the input of the control circuit. Thisposition has no impact on the operation of the current limiter. Becauseof this, the current limiting function is provided as soon as thecurrent limiter is in series with the switching element and thecapacitor. This position also has no effect on the conducting state. Itwould be possible to measure the voltage controlling the conductingstate at the terminals of the series circuit of the current limiter, ofthe switching element and of the condenser, without this changing theoverall operation of the device described in FIG. 1. This is becausewhen the switching element is not conducting, the voltage at theterminals of the voltage limiter is zero. It would therefore be possibleto place the voltage limiter, or a part thereof, between the inputterminal of the control circuit and the switching element.

However, the proposed position of the voltage limiter has the advantageof providing, in the circuit of FIG. 4, the cumulative effect describedabove. If the voltage limiter or a part thereof is placed between theinput of the control circuit and the switching element, the circuit doesnot benefit from this cumulative effect.

The converter of FIGS. 1, 3 and 4 enables a simple measurement of theconsumption, and simple data transmission along the power supply line tothe converters. This measurement and this transmission could also beimplemented with known converters. Their implementation would be mademore complex, to the extent that these converters of the prior art donot have a conducting state which is known in advance at any precisemoment, like those described above.

The description given with reference to FIG. 9 onwards in the example offull-wave rectification is also applicable to the example of half-waverectification.

Specific embodiments of an unregulated electrical converter according tothe present invention have been described for the purpose ofillustrating the manner in which the invention may be made and used. Itshould be understood that implementation of other variations andmodifications of the invention and its various aspects will be apparentto those skilled in the art, and that the invention is not limited bythe specific embodiments described. It is therefore contemplated tocover by the present invention any and all modifications, variations, orequivalents that fall within the true spirit and scope of the basicunderlying principles disclosed and claimed herein

What is claimed is:
 1. A voltage converter with input terminals, havinga series circuit between the input terminals, the series circuitcomprising: a switching element and a capacitor, the discharge of thecapacitor supplying an output voltage of the converter, and a controlcircuit adapted to cause the switching element to conduct when an inputvoltage is less than a first threshold, irrespective of the outputvoltage, and adapted to cause the switching element not to conduct whenthe output voltage is greater than a second threshold, irrespective ofthe output voltage, wherein the first threshold is higher than thesecond threshold.
 2. The converter of claim 1, further including ahalf-wave or full-wave rectifier, the output of which supplies theseries circuit.
 3. The converter of claim 1, further including a currentlimiting element in series with the series circuit.
 4. The converter ofclaim 1, wherein the switching element is a MOS transistor.
 5. Theconverter of claim 1, wherein the switching element further includes aninput terminal, an output terminal, and a control terminal; a controlvoltage supplied by the control circuit and applied between the controlterminal and the output terminal; and wherein the switching element hasa substantially constant conducting threshold between the controlterminal and the output terminal, the switching element conductingbetween the input terminal and the output terminal when the conductingthreshold is reached.
 6. The converter of claim 5, wherein the controlcircuit has a single input connected to one terminal of the seriescircuit, one output connected to the control terminal of the switchingelement, and wherein the other terminal of the series circuit isconnected to ground.
 7. The converter of claim 6, wherein the controlcircuit further includes a voltage source driven by said single input,the voltage source adapted to deliver a voltage which remainssubstantially constant while the input voltage is greater than a firstthreshold, and otherwise decreases; a second capacitor, one terminal ofwhich is connected to ground, and a controlled inverter, an inputterminal of which is connected to the other terminal of the secondcapacitor, and which is adapted to selectively connect the secondcapacitor to the voltage source in a first position, and to the outputof the control circuit in a second position.
 8. The converter of claim7, wherein the controlled inverter is adapted to toggle from the firstposition to the second position when the voltage delivered by thevoltage source decreases.
 9. The converter of claim 7, wherein thecontrolled inverter is adapted to toggle from the second position to thefirst position when the output voltage is greater than a secondthreshold.
 10. The converter of claim 7, wherein the controlled inverteris adapted to toggle from the second position to the first position whena difference between the output voltage of the control circuit and theoutput voltage of the converter is less than the voltage threshold ofthe switching element.
 11. The converter of claim 7, wherein thecontrolled inverter further includes a first diode between the voltagesource and the second capacitor; a second transistor of the bipolartype, an emitter of which is connected to the second capacitor, and acollector of which provides the output of the control circuit; and aresistor between the voltage source and a base of the second transistor.12. The converter of claim 11, wherein the voltage source furtherincludes a Zener diode connected between ground and an anode of thefirst diode, wherein the Zener diode is connected to the input of thecontrol circuit through a resistor, and said Zener diode placed inparallel with a second resistor.
 13. The converter of claim 1, furtherincluding means for measuring a temporal position of at least onefalling edge of a control voltage applied to the switching element. 14.The converter of claim 1, further including means for measuring a valueof the output voltage, the means for measuring being controlled by acontrol voltage applied to the switching element.
 15. A circuitcomprising: a voltage converter with input terminals, the voltageconverter including a series circuit between the input terminals, theseries circuit including a switching element and a capacitor, thedischarge of the capacitor supplying an output voltage of the voltageconverter; a control circuit adapted to cause the switching element toconduct when an input voltage is less than a first threshold,irrespective of the output voltage, and adapted to cause the switchingelement not to conduct when the output voltage is greater than a secondthreshold, irrespective of the output voltage, wherein the firstthreshold is higher than the second threshold; and a load fed by theoutput voltage of the converter.
 16. The circuit of claim 15, whereinthe load is adapted to generate over-consumption.
 17. The circuit ofclaim 16, wherein the load has at least one passive element selectivelysupplied by the output voltage.
 18. A device having at least onecircuit, the at least one circuit comprising: (a) a voltage converterwith input terminals, the voltage converter having a series circuitbetween the input terminals, the series circuit including a switchingelement and a capacitor, the discharge of the capacitor supplying anoutput voltage of the voltage converter; (b) a control circuit adaptedto cause the switching element to conduct when an input voltage is lessthan a first threshold, irrespective of the output voltage, and adaptedto cause the switching element not to conduct when the output voltage isgreater than a second threshold, irrespective of the output voltage,wherein the first threshold is higher than the second threshold; (c) aload fed by the output voltage of the converter; and the device having acurrent sensor configured to sense current supplied to the voltageconverter.
 19. The device of claim 18, wherein the current sensor sensesa width of current pulses.
 20. The device of claim 18, wherein thecurrent sensor senses a time separating current pulses.
 21. A method oftransmitting data from a load connected to a conversion device, themethod comprising the steps of: (a) providing a voltage converter withinput terminals, the voltage converter including a series circuitbetween the input terminals, the series circuit including a switchingelement and a capacitor, the discharge of the capacitor supplying anoutput voltage of the converter; a control circuit adapted to cause theswitching element to conduct when an input voltage is less than a firstthreshold, irrespective of the output voltage, and adapted to cause theswitching element not to conduct when the output voltage is greater thana second threshold, irrespective of the output voltage, wherein thefirst threshold is higher than the second threshold; (b) connecting theload to the voltage converter so that the output voltage of the voltageconverter is supplied to the load; (c) varying a power consumption ofthe load; and (d) detecting a variation in a temporal position of atleast one current pulse in a current input to the voltage converter. 22.The method of claim 21, wherein the step of detecting further includesdetecting a variation in a temporal width of at least one current pulse.23. The method of claim 21, wherein the step of detecting furtherincludes detecting a variation in a time between a falling edge of acurrent pulse and a rising edge of a following current pulse.
 24. Themethod of claim 21, wherein the step of varying is carried out upon analarm condition.